For example, each of JP-A-2002-21625 and JP-A-2004-150319 discloses an exhaust recirculation apparatus (exhaust purification apparatus) for an internal combustion engine. Each exhaust recirculation apparatus performs high-pressure exhaust gas recirculation (high-pressure EGR) and low-pressure exhaust gas recirculation (low-pressure EGR). In the high-pressure EGR, exhaust gas is distributed from the upstream of a turbine of a turbocharger in an exhaust system, and recirculated into the downstream of a compressor of the turbocharger in an intake system. In the low-pressure EGR, exhaust gas is distributed from the downstream of the turbine in the exhaust system, and recirculated into the upstream of the compressor in the intake system. The exhaust recirculation apparatus switches between a combination EGR range, in which performing both the high-pressure EGR and the low-pressure EGR, and a low-pressure EGR range, in which performing only the low-pressure EGR, in accordance with load applied to the engine, or the like.
For example, in JP-A-7-293347, the exhaust recirculation apparatus obtains an EGR ratio of exhaust gas recirculation in accordance with change in an intake air mount when the exhaust gas recirculation (EGR) is started and terminated. The exhaust recirculation apparatus corrects a relationship between the EGR ratio and a control amount of the EGR in accordance with the EGR ratio. Thus, the exhaust recirculation apparatus is capable of accurately controlling the EGR. However, the exhaust recirculation apparatus in JP-A-7-293347 is provided to the engine having one EGR system, not having both of a high-pressure EGR system and a low-pressure EGR system.
An exhaust recirculation apparatus may be provided to an engine having both of a high-pressure EGR system and a low-pressure EGR system. However, in this structure, it is difficult to accurately control the amount of EGR around switching between the combination EGR range, in which both the high-pressure EGR and the low-pressure EGR are performed, and the low-pressure EGR range, in which only the low-pressure EGR is performed. Accordingly, in general, emission increases around the switching between the combination EGR range and the low-pressure EGR range.